An I/O control unit (CU), such as used to control the operation of a direct-access storage device (DASD) or other devices, can provide optional facilities that require specific host system support and are therefore enabled by the host system. These Host Enabled Facilities (HEFs) are enabled when the host system communicates them to the CU over the I/O interface. Certain CU or path-related events can cause the CU to lose its knowledge of a HEF, which requires the host system to communicate it to the CU again.
One typical problem caused by such loss may be that the host system may not be aware that the CU has lost knowledge of the HEF. The CU does not notify the host system when this condition occurs. Because this condition occurs infrequently, it would be inefficient for the host to poll the CU for this condition.
The impact of the CU losing knowledge of the HEF can be significant, at least because this may cause the CU to “turn off” the facility. The host system not only must re-enable the HEF it supports, but may need to recover from resulting error conditions and redo any initialization processes required for using the HEF. As a specific example, parallel access volume (PAV) capability such as HyperPav is a HEF supported by z/OS. If the relevant CU loses knowledge of the HEF, HyperPav alias devices can get I/O errors and be marked unusable. In this circumstance, the operating system must recover these alias devices and redo HyperPav alias initialization.
Accordingly, it is an object of the present invention to provide a method and system to correctly and efficiently detect loss of CU knowledge of a host enabled facility while lessening or eliminating any additional overhead associated with unnecessary initialization processes.